In laboratories, operation rooms and food processing facilities, workers who are wearing protective gloves may have difficulty in opening a sealed plastic bag with or without re-closable zipper feature. The workers may prefer opening a plastic bag without using both hands to pull open a sealed re-closable zipper or conventional bag with seal or using any sharp tool to cut open a sealed bag. Regular consumers may also prefer opening a sealed plastic bag without using any cutting tool.
Re-closable bags have long history of development and currently, mainly three different types of process are used to manufacture the re-closable bags. A blown film process with zipper profiles extruded together with main film web was first described in U.S. Pat. No. 3,338,284 to Ausnit, U.S. Pat. No. 3,852,386 to Behr, and U.S. Pat. No. Re. 29,208 to Naito. A second approach is a zipper attached process. In this process, zipper profile was extruded separately either pre-cooled or in line and then attached with pre-extruded film or laminated film using thermal method or adhesive technology. This process can be seen in U.S. Pat. Nos. 3,226,787 and 4,101,355 to Ausnit, U.S. Pat. No. 3,846,209 to Howard; U.S. Pat. No. 3,904,468 to Noguchi, U.S. Pat. No. 4,279,677 to Takahashi, and U.S. Pat. No. 4,582,549 to Ferrell. Another approach is a casting process with zipper profile extruded together with the web and has been described in U.S. Pat. No. 3,462,332 to Goto, U.S. Pat. No. 4,295,919 by Sutrina, U.S. Pat. No. 4,306,924 and U.S. Pat. No. 4,428,788 to Kamp, U.S. Pat. No. 4,522,678 to Zieke, and U.S. Pat. No. 4,555,282 to Yano.
Laminated sheet was proposed by Flor and Lucchetti in U.S. Pat. No. 3,075,857 using a polypropylene sheet as substrate coated with a polyvinyl alcohol layer to provide oxygen and moisture barrier properties and a binder layer. More laminates between polymeric sheet and metal using binders were disclosed in U.S. Pat. Nos. 3,481,812, 3,663,334 and 3,669,797. Laminates between two polymeric sheets using binders were also disclosed in U.S. Pat. Nos. 3,607,616, 3,697,368, 3,922,473 and 4,163,080.
There are different methods to create easy tear strip on a polymeric bag. A popular one is to use a notch or a cut line on the seal edge of a bag made by laminated film which contains at least one biaxial oriented film on the laminated film. For a single layer polymeric bag, a pre-cut short line or notch or a perforation line is widely used to create an easy to tear feature. However, a notch or a pre-cut short line on the seal edge of a single layer polymeric bag cannot provide a straight tear line and the perforation line on a bag may not provide contamination protection to the content inside the bag. Rohde described a tear strip for envelop and polymeric bag using a coextruded color band of different material in U.S. Pat. Nos. 3,535,409 and 3,368,740. However, the colored tear strip has no bonding force with either side of the main bag body since they are formed by different material and the main bag body was disconnected by the tear strip section. The film made by this method has no mechanical strength to adhere its color strips with either side of the main bag body and are not practical.
In recent year, Taheri described a process of making a thin section on the main polymeric bag body to provide a weak and easy tear zone in U.S. Pat. Nos. 6,149,302 and 6,217,216 B1. In this process, Taheri described that the thin section creates a stress difference and tends to have film web wrinkle problem and needs to add at least one, preferably two, polymeric strips to provide added weight and strength to reduce the lateral forces acting in the thin section. These stabilizing strips can be used to define the tear zone. The wrinkle problem created by the thin section was reduced after adding two polymeric strips. However, the wrinkle and the difficulty to wind still exist and generate waste and other production problems.
The disclosed plastic bags are directed at solving one or more problems set forth above and other problems.